In general, multilayer circuit boards are utilized in high power applications such as motor controllers, computers, power supplies, or other control devices. Typically, these boards include high-power electrical devices such as resistors and semiconductors to perform the functions required by the associated applications. As a result, these electrical devices often generate a significant amount of heat, and require heat sinks or other thermal management systems to prevent the circuit boards and electrical devices from overheating.
Heat sinks are typically metal components relatively large in size and secured to circuit boards or associated electrical devices to enhance heat dissipation therefrom. In particular, heat sinks are attached to a thermally and electrically conductive portion of an electrical device. For example, heat sinks are frequently secured directly to the lead frame of the device with hardware such as brackets, bolts, or other mountings. This additional hardware is expensive and increases the assembly time for the circuit board. The heat sinks are often electrically isolated from the lead frame with a heat conducting, electrically insulating layer of film or other material which is placed between the electrical device and the heat sink. Such a layer is disadvantageous because installing the layer increases the assembly time for the circuit board. In addition, depending on the material and its thickness, this insulating layer can create an undesirable thermal resistance layer. Furthermore, the integrity of the layer is very difficult to inspect.
Some electrical devices are packaged as surface mount devices which utilize a minimum amount of space on the circuit board. However, higher power surface mount devices must be mounted on or near large pads or sections of a metal layer on the circuit board to provide adequate heat dissipation. These large sections are disadvantageous because the space required by the large sections could otherwise be utilized by other electrical components. To reduce the size of these large sections, surface mount devices are often mounted on circuit boards made from ceramic, epoxy/alumina covered metal base plates, or other materials which have a high thermal conductivity. Drawbacks with ceramic circuit boards include their expense, brittleness and weight.
Thus, there is a need for a multilayer circuit board having an insulated mounting area for a surface mount device and a heat sink. There is also a need for a low cost insulated mounting for a heat sink which requires a small amount of board space and is thermally conductive.